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From "Bert Huijben" <b...@qqmail.nl>
Subject RE: svn commit: r1715228 - /subversion/trunk/subversion/libsvn_ra_serf/util.c
Date Thu, 19 Nov 2015 22:48:49 GMT


> -----Original Message-----
> From: Bert Huijben [mailto:bert@qqmail.nl]
> Sent: donderdag 19 november 2015 23:41
> To: 'Ivan Zhakov' <ivan@visualsvn.com>
> Cc: dev@subversion.apache.org
> Subject: RE: svn commit: r1715228 -
> /subversion/trunk/subversion/libsvn_ra_serf/util.c
> 
> 
> 
> > -----Original Message-----
> > From: Ivan Zhakov [mailto:ivan@visualsvn.com]
> > Sent: donderdag 19 november 2015 23:12
> > To: Bert Huijben <bert@qqmail.nl>
> > Cc: dev@subversion.apache.org
> > Subject: Re: svn commit: r1715228 -
> > /subversion/trunk/subversion/libsvn_ra_serf/util.c
> >
> > On 20 November 2015 at 00:03, Bert Huijben <bert@qqmail.nl> wrote:
> > >> -----Original Message-----
> > >> From: rhuijben@apache.org [mailto:rhuijben@apache.org]
> > >> Sent: donderdag 19 november 2015 19:03
> > >> To: commits@subversion.apache.org
> > >> Subject: svn commit: r1715228 -
> > >> /subversion/trunk/subversion/libsvn_ra_serf/util.c
> > >>
> > >> Author: rhuijben
> > >> Date: Thu Nov 19 18:03:11 2015
> > >> New Revision: 1715228
> > >>
> > >> URL: http://svn.apache.org/viewvc?rev=1715228&view=rev
> > >> Log:
> > >> Add a tiny bit of code to allow testing with Apache Serf's http/2 support.
> > >>
> > >> I committed this patch to celebrate that I got through basic_tests.py
> > >> using the current http/2 support.
> > >>
> > >> * subversion/libsvn_ra_serf/util.c
> > >>   (conn_negotiate_protocol): New function.
> > >>   (conn_setup): Register usage of conn_negotiate_protocol when
> > >>     a very recent (read: trunk) serf + SVN__SERF_TEST_HTTP2 are used.
> > >
> > > Currently most tests pass for me over http2 when running with some
> minor
> > tweaks. I still get some aborted connections that aren't retried as cleanly as
> > with http 1.1. Not sure what causes these yet; but this could also be an
> httpd
> > issues.
> > >
> > > The only ra function that really causes problems is the implementation of
> > the replay
> > > range api. This 100% expects that results will be received in the same
> order
> > in which
> > > they are sent. This is typically the correct way in http 1.1 using serf, but
> > even there it
> > > is sometimes possible to get results out of order. (Authentication can re-
> > queue
> > > requests... and sometimes authorization is necessary even when earlier
> > requests
> > > succeeded, depending on the auth scheme).
> > >
> > Can we use WINDOW_UPDATE frame to control flow of replay-revision
> > response? In this case we can use spillbuf for buffering responses to
> > avoid latency performance regressions. What do you think?
> 
> In theory we could... we could set the initial window to 0 and then send a
> window update later. Assuming that httpd does that efficiently, etc. etc.
> (Some of these assumptions are most likely not true)
> 
> But I doubt if it would be more efficient than just sending the request when
> we need it... or perhaps asking the properties a revision earlier. (We can also
> send the request, but just leave out the end of stream marker... Sending EOS
> will then handle the request)

The proper 2.0 way would be to make the streams completely dependent on each other via priority
handling.

But using this priority information is optional on the server side. And I doubt that we can
trust this to always do the right thing even if httpd would implement this correctly today.

	Bert


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